1. Field of the Invention
The present invention relates to an optical element module, and more particularly to an optical element module package having a TO-can structure and a method for manufacturing the same.
2. Description of the Related Art
In general, an optical element module, mounted on an electric circuit device (e.g., a printed circuit board), modulates radio-frequency signals into optical signals. Due to a rapid development in the information industry, there is an increasing trend to transmit information by means of an optical communication network as a result of faster and larger data capacity demands. Traditionally, a TO-can structure package has been used in inexpensive optical element modules and is now also being applied to fast, large-data capacity optical element modules.
FIG. 1 is a perspective view showing a conventional optical element module package 100 having a TO-can structure. As shown, the optical element module package 100 includes a stem 101 having a heat sink block 111 protruding from one end thereof and a plurality of leads 102 at the other end. The leads 102 are comprised of a laser diode anode lead, a laser diode 103, a cathode lead, a photo diode anode lead 102, and a photo diode cathode lead 102. In general, the laser diode anode lead is electrically connected to the stem 101, RF signal, combined with DC bias current by external bias-tee is inputted to laser diode cathode lead. The laser diode 103 and the photo diode 104, which detects light emitted from the laser diode 103, are installed on the stem 101. The laser diode 103 is mounted on the heat sink block 111, and the laser diode 103 and the photo diode 104 are connected with the corresponding leads 102 via a wire bonding method.
The leads 102 are coaxially aligned with the respective through-holes 113 extending through the stem 101 therethrough. The through-holes 113 are then filled with a sealant 105 of a glass material. The sealant 105 is melted to hold the leads 102 together with the stem 101 and to seal the through-holes 113 at the same time.
The above package having a TO-can structure is available from Luminent Inc. and distributed under a product named “C-13-DFB10-TJ-SLC21”. However, this type of optical element package is not suitable for a high-speed transmission above several Gbps because the package may suffer from an inherent inductance of its leads, a parasitic capacitance between its leads and stem, and a characteristic impedance mismatch that may occur while radio-frequency signals inputted from outside pass through the respective leads. Moreover, the manufacturing procedure is inconvenient as the respective leads must be aligned with a plurality of through-holes in the stem and the though-holes must be sealed individually.
FIG. 2 is a perspective view showing another conventional optical element module package 200, which has a TO-can structure using a ceramic feedthrough. As shown, the optical element module package 200 includes a stem 201 having a heat sink block 211 protruding from one end thereof and a ceramic-laminated feedthrough 203 inserted into the stem 201. The feedthrough 203 is positioned on the heat sink block 211 and has a coplanar waveguide (CPW) 202 formed on its surface. The CPW-type package 200 receives radio-frequency signals from outside via leads 204. This type of CPW-package is sold under the product name of “TO TX PKG A2527” by Kyocera Corp.
The above package has some drawbacks. First, the feedthrough 203, having a ceramic-laminated structure, is formed through a low temperature co-fired ceramic (LTCC) process at the temperature up to 800–1000° C. Such a high temperature process increases the manufacturing cost. In addition, it is difficult to guarantee a hermeticity between the feedthrough 203 and the stem 201. Furthermore, the adhesive strength between the leads 204 and the feedthrough 203 is weak. All these factors leads to an unreliable product.